Adenovirus serotype 5 (Ad5) is the vector of choice in basic research applications, murine lung cancer models, and human gene therapy trials. Adenoviruses have a stable 36 kb double-stranded DNA genome protected by a protein capsid decorated with Ad fiber protein spikes that target infection to receptors on specific cell types. Adenoviruses do not integrate into host DNA, can be produced to high titers using established protocols, and have proven safety in human gene therapy and cancer applications. Thus, Ad-based vectors have enormous promise for cancer diagnostics and therapies.